There is a common need for highly active and stable catalysts that can be used especially in the oxidation of organic compounds such as alcohols, aldehydes, polyhydroxy compounds and mono-, oligo- and polysaccharides.
The use of supported palladium and platinum catalysts in the oxidation of glucose is known. However, this is severely limited due to the low selectivity and the low conversion rate. In addition, the catalysts are deactivated relatively rapidly as a result of a blocking of the catalyst surface due to absorption and/or due to poisoning effects.
Thus, for the commercial production of oxidation products from carbohydrates, it continues to be necessary to use fermentation processes, which are associated with high equipment expenditure and with waste water loads.
For this reason, it is necessary for new catalyst types to be developed, which will enable effective catalytic oxidation, especially of carbohydrates, for example for the production of aldonic acids using dioxygen as the oxidation agent, and which, in addition to high activity and selectivity, will have a long lifespan.
Supported gold catalysts are also known. They are used primarily in the oxidation of CO or propene in the gas phase, and for selective hydrations. Carbon-supported gold catalysts can also be used for the selective oxidation of D-glucose to D-gluconic acid in the liquid phase. Supported gold catalysts with nanodisperse distributed gold particles on carbon or metal oxide supports are also known from DE 10319917 A1. These are used primarily for the C1 selective oxidation of glucose and other carbohydrates. The activity level of these catalysts, however, is not satisfactory.
Methods for producing gold catalysts by impregnation of the support using the “incipient wetness method” are known. However, in the literature such impregnation methods are described as unsuitable for the synthesis of active gold catalysts. This is because generally these methods produce only gold particles that are too large (greater than 10 nm).